Industrial furnace and firing apparatus



Sept. 22, 1942. F, S, BLOOM 2,296,255

lNDUSTRlAL FURNACE AND FlRING APPARATUS Filed June 10, 1939 3Sheets-Sheet l FLOW INDICATOR FLow'luolcA INVENTOR F. S. BLOOM Sept. 22,1942.

INDUSTRIAL FURNACE AND FIRING APPARATUS I 3 Sheets- Sheet 2 Filed 'June10, 1959 INVENTOR Zia Sept. 22, 1942.

F. S. BLOOM LNDUSTRIAL FURNACE AND FRING APPARATUS Filed June 10, 1939 3Sheets-Sheet 3 &

INVENTOF? Patented Sept. 22, 1942 UNITED STATES PATENT OFFICE,

Frederick S. Bloom, Mount Lebanon, Pa.

Application June 10, 1939, Serial No. 278,520

8 Claims. (01. 236-15) This invention relates to industrial furnaces,

particularly to installations of one or more furnaces that are firedwith pre-mixed gaseous fuel and air.

In the operation of such furnaces, the combustible mixture is deliveredunder pressure to the burners of the furnace. Ordinarily, valves areprovided in the inlet pipes leading from the mixture supply line to theburners, and, while these valves may be manually adjusted, the essentialregulation of the rate of combustion in the furnace is obtained byvarying the pressure, with consequent variation in the quantity, of thecombustible mixture delivered to the burners. It has been found in suchfurnace operation that the capacity of the burners .is limited; that is,the range of combustion control is too narrow. If the pressure of thefuel and air mixture is reduced so far as is necessary to obtain therelato the danger point. Thus, the range of operation of the burners islimited, and it is such objectionable limitations as this that haveimpeded the otherwise advantageous use of the premix method of firing. I

The object of my invention is to provide improvements and refinements inthe structure of the burners and control instrumentalities of suchfurnaces, by virtue of which the range of com- .bustion control is sofar widened as to remove all practical limitations to the use of thepremix method of firing, and to eliminate all dangers of back-firing andexplosion. In one installation I may maintain the velocity of flow ofthe mixture at substantially constant value, while varying the quantityof the combustion-sustaining mixture delivered into the furnace. And inanother installation I may vary the velocity of the mixture flowing intothe furnace, with variation in the quantity of the mixture deliveredinto the furnace. But in either case all danger of backfiring andexplosion is eliminated. ,It is further my object to provide means tothe end that the individual burners, or selected groups of burners, maybe independently and automatically controlled in accordance withtemperature conditions within the furnace.

An embodiment of the invention is illustrated in the accompanyingdrawings, in which a typical furnace equipped with the burners andcontrol apparatus of the invention: the control apparatus is illustrateddiagrammatically, partly in elevation and partly in section.

Fig.,II is a view of my burner structur invertical section; the burneris shown-in position of service, with the wall of the furnace and theinlet pipe shown fragmentarily.

Fig. III is a view comparable with Fig. "II, illustrating partly invertical section and partly in side elevation a burner of modified form.

And Fig. IV is a diagrammatic view, showing a furnace in side elevation,and certain modifications in the apparatus for controlling combustionwithin the furnace.

Referring to Fig. I of the drawings, the reference numeral l is appliedto the furnace, which may be a batch furnace, or a continuous furnace,or a lehr, for heating or heat-treating articles formed of metal, glass,or other materials. A line of burners 2 is mounted on each of theopposite side walls of the furnace, and in service these burners areadapted to project burning columns of fuel into the furnace chamber. Thecombustible mixture of gaseous fuel and air is delivered by a supplyline 3 into a manifold l, and pipes 40 severally connect the burnerswith such manifold.

The apparatus employed for supplying the desired combustible mixtureincludes a fan 5 that delivers air under pressure into supply line 3,and a pipe 6 that delivers fuel gas under superatmospheric pressure tothe said line 3.

The quantities of fuel and air delivered to the burners (and inconsequence the rate of combustion and the temperature within thefurnace) are controlled by means of a butterfly valve 8 arranged in thesupply line 3, and in accordance with my invention, I not only providemeans for maintaining the desired ratio offuel to air in the supply line3, but I provide, in cooperative organization with such means,instrumentalities for automatically adjusting the valve 8, to establishand maintain specified temperature conditions within the furnace. Ishall first consider the matter of controlling the mixture of fuel andairthe fuel to air ratio.

It will be initially understood, of course, that in order to establishand maintain the desired efficiency of combustion in the furnace, it isessential that the ratio or proportion of fuel to air must be accuratelycontrolled. To this end a butterfly valve 1 is provided in the fuel line3. The valve 1 is automatically adjusted in accord- Fig. I is afragmentary view in perspective of 55 ance with the quantity of airflowing into line 3,

lator.

I the quantity of fuel admitted to the line 3 is regulated and thedesired ratio of fuel to air is established and maintained, and thisholds true even though there be fluctuation and variation in the flow ofeither the fuel or the air.

Means for so automatically controlling the mixture of fuel and air are,as has already been mentioned, known to the art, and in exemplary way Ishall briefly describe a widely used piece of apparatus known as theAskania ratio regu- Such regulator includes a plunger 9, inresponse towhose movement in a pneumatic cylinder II), in one direction or theother, the valve 1 is opened or closed a greater or less degree,depending upon the magnitude of plunger movement. The movement of theplunger is determined and controlled by the pressure diiferentialbetween the fuel and the air. Specifically, orifice plates II and I2 arearranged in the air and fuel lines, respectively. Tubes [3 and I4 leadfrom opposite sides of each orifice plate to the opposite sides of aflexible diaphragm I5, and, as shown, the two diaphragms I5 are arrangedin opposing relation, each standing in open communication on oneside-the side that communicates with the low pressure side of theorifice plate (II or I2)with a pressure chest l6, from which chest twotubes I1 and I8 extend, one to each of the opposite ends of thevalve-operating cylinder l0. Within the chest IS a counterpoised leverl9 and jet-pipe 20 are arranged to swing in response to the movement ofthe diaphragms, and in known way the delicately counterpoised jet-pipesways into and stands in a position that is determined by the aggregateeffect of the gas and air pressures upon the two diaphragms IS. Theposition of the distal end of the jet-pipe in known manner determinesthe relative pressures of fluid in the two tubes IT and I8, and, as thepressure is augmented in one tube or the other, the plunger 9 incylinder 10 is caused to move in one direction or the other. Thus, thevalve 1 is swungtowards open or closed position, according as thepressure of the air (that is, the quantity of air flowing throughorifice plate II) increases or decreases relatively to the pressure(quantity) of fuel gas flowing through orifice plate l2. Theautomatically adjusted valve 1 makes compensation in the. rate of fiowof the fuel for variations in the rate of flow of the air, and so thedesired ratio of air to fuel is accurately maintained, irrespective ofthe quantity of the mixture of air and'fuel that, under the control ofvalve 8, flows to the burners 2. Needless to say, the ratio regulatormay be provided with the usual means (2|) for varying the value of theratio of air to fuel which is maintained, but this specification neednot be concerned with such known matters of detail.

It will be perceived that, if the butterfly valve 8 is moved towardsclosed position, the fan 5 will deliver lessair, and that in consequencethe flow of air through orifice I I will decrease, whereupon theapparatus Il-2l will operate immediately to shift the valve 1 anddecrease the flow of gas. Upon such movement of the master valve 8towards closed position, the pressure of the gaseous mixture in themanifold 4 will drop, and, as presently will appear, certain valves inthe bumers 2 will automatically close a corresponding degree, whereby,although the pressure and volumetric rate of flow of the combustiblemixture are decreased, the velocity of flow from the burners will bemaintained at sufllciently high value to prevent back-firing. v

In accordance with the invention, the firing of, or rate of combustionwithin, the furnace is caused to function automatically, under theinfiuence of the temperature conditions within the furnace.

To this end, I organize an electric motor 22 with the valve 8; thismotor is energized by a circuit 23, leading from an electric pyrometer24; pyrometer 24 is connected, by leads 25, to a suitable source ofelectric energy (not shown); and the pyrometer is subject in itsoperation to a theremocouple 26 which, connected by a circuit 21 to saidpyrometer, is exposed to the temperature within the furnace. Thoseskilled in the art are familiar with the construction and operation ofeach of these instrumentalities; they can obtain them on the openmarket; and inasmuch as my invention lies in the organization of suchinstrumentalities with apparatus of the sort above described, and withburners of the particular construction presently to be described, itwill suflice to describe the operation of the devices 22, 24, 26generally.

When the temperature in the furnace rises, the usual electro-thermalcurrent flowing in circuit 21 increases in value; when the temperaturerises through a certain increment the increased current becomeseffective 'momentarily to close a relay in the pyrometer 24, and theclosing of the relay effects the energizing of the circuit 23; under theinfluence of such momentary flow of current in circuit 23 the armatureof motor 22 moves through a predetermined interval, and swings the valve8 through a predetermined interval towards closed position. thetemperature in the furnace continues to rise, the apparatus repeats theoperation, until the valve 8 is adjusted in the position at which therate of fuel delivery and the rate of combustion are reduced to thepoint at which the rise in temperature is arrested. If the temperaturein the furnace falls below critical value, the thermoelectric currentdecreases in value and such decreasein current in circuit 21 effects theclosing of a different relay in the pyrometer 24, with the consequenceand effect that an energizing current flows in reverse direction incircuit 23, and causes the motor 22 to step the valve 8 into more widelyopened position. In this way the quantity of the combustible mixturesupplied to the furnace is increased, and the 'fumace' temperatureelevated. Thus, the valve 8 operates automatically (in conjunction withthe ratio-regulating apparatus already described) to regulate the rateor intensity of combustion, in such manner that the desired temperatureconditions are established and maintained in the furnace. And it will bemanifest that by proper selection and adjustment of the thermocouple andpyrometer, the temperature at which the furnace is maintained may bevaried to suit the work.

Turning to Fig. II, the construction of my improved burners will beconsidered. Each burner consists in a metal housing 28 adapted to bemounted, as shown, on the furnace wall, with the outlet orifice 29 ofthe burner in registry with the mouth of a conical passage 30 in therefractory port-block 3| which, as usual, is embodied in the furnaceside wall. The combustible mixture of fuel and air enters the housing byWay of pipe 40, and within the housing a valve 32 is arranged to controlthe flow through orifice 29.

It will be understood that in service the com- If, thereafter,

bustion of the mixture streaming through orifice 29 and port-block 3|into the furnace is initiated in the conical passage 30 in theport-block, and that so long as the velocity of the streaming gases isabove a certain critical value, there is no danger of the flame burningback through the orifice 29 and causing premature combustion andexplosion in the burner body 23 or in the supply pipe 40. With this inmind, it is to be understood thatmy burner structure includes,advantageously, means for adjusting the valve 32, in accordance withvariations in the-pressure of the combustible mixture supplied to theburner, so that, regardless of the pressure at which the combustiblemixture enters the burner, the ve-.

locity offiow through the orifice 29 will either be held above criticalvalue, or the valve 32 ;will close.

Such means may, as shown in Fig. 11, consist in a flexible diaphragm 33,to which the stem 34 nect a line 39 to the diaphragm chest in theburner, as shown. 'This line constitutes in the burner structure anauxiliary inlet for fluid under pressure; and provides means whereby aregulatory pressure may be established in the burner,

and used in the control of burner operation. In

. creasing or decreasing the pressure of the air in of valve 32 issecured. A spring 35,-whose eflective force may be adjusted by means ofa screw 35, bears upon one side of the diaphragm and tends to shift therod 34 in right-to-leit direction and to move the valve 32 towardsclosed position,

while the pressure of thecombustible mixture, transmitted through apassage 66 in partition 31,

is effective on the opposite side of the diaphragm, and, opposing theforce of spring 35, tends to move the valve into more widely openedposition. As in s vice the pressure of the combustible mixture suppliedto the burner rises or falls, under the automatic combustion-controllingregulation of valve 8 (Fig. I), the valve 32 is shifted to the right orto the left, and accordingly increases or decreases the effective areaof the orifice 29, with the consequence that the velocity of the gasesflowing through the port-block 3| is maintained above criticalvalue--above the value at which the flame can work back through theorifice 29 and cause premature combustion in the burnerbody 28.

If the pressure of the combustible mixture should drop to a value atwhich a safe velocity through orifice 29 cannot be maintained, the valve32, under the urging oi spring 35, moves into fully closed position, andin such position it is effective, obviously, to prevent backfiring.Manifestly, it is merely a matter of properly adjusting the effectiveforce of spring 35 to insure noted, includes one or more small passages38,

which, when the valve is in closed position, permit the flow of a slightbut suflicient quantity of the combustible mixture into the throat ofthe port-block, to sustain a pilot flame.

It is important to note that the valve 32 is arranged to control theflow of the combustible mixture, not at some point in the line of flowremoved a substantial interval from the inlet end of the passage 29, 30,but immediately at the inlet end of such passage, and preferablyimmediately at the inlet end 39a of the conical throat of the port-block3|. As will be perceived in Fig. II, when the valve 32 is seated inexplowill prove valuable in burners that are manually controlled, or arecontrolled by means other than those illustrated and described herein.

In refinement of the structure described, I conline 39, the total effectof the pressures on the righ-hand side of the diaphragm may be increasedor decreased, and the valve 32 controlled at will. The pressure in line39 may be regulated at a station more or less remote from the furnace.In some cases, the springs may be dispensed with, and the operation ofthe burners made subject to pneumatic pressures alone. All of theburners oi the furnace, or various groups of burners, may by the use ofa manually operated air valve be made entirely responsive to the will ofthe attendant, or they may be caused to operate automatically, as firstdescribed. And

additionally it is to be noted that the pressure of air supplied by pipe39 may be governed and held to a value that will provide (either with orwithout a spring 35) such pressure on the righthand side of thediaphragm 33 as will effect the desired automatic operation of the valve32. The pneumatic lines 39 of the several burners may be subject to asingle control valve, so that the operation of all burners may besimultaneously regulated or varied.

In Fig. .111, I illustrate a modification in the means that control theburner valve. Specifically, I show a Sylphon or metal bellows 33a, whoseinner head 33b is secured and sealed to the valve-stem 34a, andwhoseouter head 330 includes a threaded plug 33a,the counterpart of the screw33 of the first-described burner, which is adapted to adjust the forceof a compression spring 35a arranged within the Sylphon and bearingagainst the inner face of the Sylphon and contracts with variations inthe pressure of the gaseous mixture to which it is exposed within theburner body 23a, and in consequence the valve 32a operates in the samegeneral manner as the valve 32.

In Fig. IV, I show that the master control valve 8 (Fig. I) may beeliminated in certain installations, and that the valves (32, Fig. II)of the several burners may serve not only as the backfire-preventinginstrumentalities but as the combustion control means as well. Morespecifically, the pneumatic control leads 39 of the burners may beconnected to a pyrometer that controls pneumatic pressure (rather thanan electric current) for regulation of the rate of combustion in thefurnace.

Sometimes it is desirable to provide diflerent rates of combustion atdifferent points in the extent of the furnace, and, if such be the case,the burners 2 will be arranged in a plurality of groups that areseverally responsive in operation to a plurality of pyrometers. Theburners 2 of the furnace la in Fig. IV are shown to be arranged in threegroups of three burners each, and the pneumatic control leads 39 of theburners in each group are connected in common to the control pipe ll ofa pneumatic pyrometer 24a. A thermocouple 26a is by a thermo-electriccircuit 2111 connected to each pyrometer, and the several pyrometersare, by leads 25b and a line 25a, connected to a source of compressedair or other gas or fluid. The pyrometers include valves (not shown)that open and close in response to the increase and decrease of thethermo-electric currents in circuits 21a, and, as such valves in thepyrometers open and close, the fluid pressure in pipes 4| leading to theburner-controlling diaphragms (33, Fig. II) correspondingly rises andfalls; that is to say, as the temperatures rise or fall (in the regionsof the furnace into which thermocouples 26a extend) the pressures on theburner diaphragms increase or decrease, and in consequence shift theburner valves either towards closed positions or into more widely openedpositions, and thus regulate the quantity of the fuel and air mixturedelivered into the furnace. In organizing the burners in groupsseverally controlled by pyrometers that are individually responsive tothermocouples arranged at successive points longitudinally of thefurnace, the temperatures at such points or regions of the furnace maybe accurately maintained; that is, the desired temperature gradient inthe furnace or lehr may be established and maintained.

The apparatus admits of great versatility in the matter of temperatureregulation. The grouping of the burners may be quickly altered toprovide the desired temperature gradient from one end of the furnace tothe other; one burner on each side of the furnace may be connected toone pyrometer and flve burners on each side may be connected to another,and so on; indeed, all

burners may be connected to a single pyrometer, if the conditions shouldrequire a single control. This interchangeability of burner grouping ismade practical and economical, due to the ease with which the smalltubing 39 and 4| may be taken apart and re=cnnected in such way as toprovide the desired burner grouping.

As illustrated diagrammatically in Fig. IV, the apparatus for supplyingthe fuel and air in proper proportion may be the same apparatus as thatdescribed in Fig. I. There is, however, an additional safety feature tobe specifically considered, and this feature is applicable to either ofthe furnace installations described. It consists in an automatic valve42 (Fig. IV) arranged in the fuel supply line. If for any reason thepressure of the (Fig.1) or pressure lines 39 (Fig. IV), the pressureswhich are effective in the control of the burner valves 32.

Many advantages in addition to those mentioned are enjoyed in thestructure of my invention; advantages in the matters of safety, controlof combustion, range of furnace temperature control, uniformity of jetvelocity (if desired), uniformity in distribution of heat in thefurnace, and variation in jet velocity (if desired). And it is to beunderstood that within the terms and intent of the appended claims, manymodifications and refinements are permissible.

Notice is hereby given of my copending application Serial No. 377,282,filed February 4, 1941.

I claim as my invention 1. A pre-mix firing system for industrialfurnaces including a plurality of burners provided severally withoutlets in communication with the combustion chamber of the furnace, aduct with which said burners communicate, means for maintaining amixture of air and fuel in said duct, a master valve arranged to controlthe flow of the mixture from the duct to said burners, means responsiveto temperature conditions within the furnace for adjusting the positionof air, or of the combustible mixture, should fall to the danger pointthe valve 42 closes and completely shuts ofi the supply of fuel. The fan5 will continue in operation, and in such case will tend to scavenge thelines 3a and 4a of the combustible mixture therein. Accordingly, if oneor more of the burner valves should fail to close when-the pressure ofthe mixture falls below critical value, the valve 42 closes and providesa safeguard against explosion. I have shown the valve 42 as a lmow typeof pneumatically operated valve, adapted in known way to close thefuelline when the pressure of the gases in pipe 3a. falls below criticalvalue.

In the foregoing specification, I have described in exemplary wayapparatus which embody the invention, and it will be understood that thediaphragm 33 and Sylphon 33a are exemplary of the pneumatic (orhydraulic devices, or the movable members of such devices, that may beused in the automatic control of the valve 32 of each burner. Thepyrometers 24 and 24a will.be understood to be 'instrumentalities which,connected to a source of energy (0. f. 25 or 25a), are responsive to thethermo-electric currents of the thermocouples 26, 26a for regulating,either through valve 8 said valve and regulating the pressure of themixture flowing from the duct to said burners, means for maintaining atsubstantially predetermined value the ratio of air to fuel in saidmixture while the position of said valve is so adjusted in accordancewith temperature conditions within the furnace, and means in each burnerresponsive to variations in the pressure of the mixture delivered to theburners for regulating the flow of the mixture through the outlets ofthe burners.

2. A pre-mix firing system for industrial furnaces including a pluralityof burners provided severally with outlets in communication with thecombustion chamber of the furnace, a duct with which said burnerscommunicate, means for maintaining a mixture of air and fuel in saidduct, a master valve arranged to control the flow of the mixture fromthe duct to said burners, means responsive to temperature conditionswithin the furnace for adjusting the position of said valve andregulating the pressure of the mixture flowing from the duct to saidburners, means for maintaining at substantially predetermined value theratio of air to fuel in said mixture while the pressure of the mixtureflowing to said burners is so regulated, and means for the prevention ofexplosive back-firing in the system, said means being organized withsaid burners severally and responsive to a drop in the pressure of saidmixture to critical value.

3. A pre-mix firing system for an industrial furnace including a burnerhaving an outlet in communication with the combustion chamber of saidfurnace, a duct communicating with the burner, means for maintaining amixture of air and fluid fuel in said duct, a valve arranged to controlthe flow of the'mixture from said duct to said burner, means responsiveto temperature conditions within the furnace for adjusting the positionof said valve and regulating the pressure of the mixture flowing fromthe duct to the burner, means for maintaining'at substantially constantvalue the ratio of air to fuel in said mixture while the pressure of themixture flowing to said burner is so regulated, and means responsive tovariations in the pressure of the mixture delivered to said burner forregulating said furnace, a duct communicating with the burner, means formaintaining a mixture of air and fluid fuel in said duct, a valvearranged to control the flow of the mixture from said duct to saidburner, means responsive to temperature conditions within the furnacefor adjusting the position of said valve and regulating the pressure ofthe mixture flowing from the duct to the burner, means for maintainingat substantially constant value the ratio of air to fuel in said mixturewhile the pressure of the mixture flowing to said burner is soregulated, and means organized with said burner for safeguarding theburner and the system from explosive backfiring of the mixture.

5. A pre-mix firing system for industrial furnaces including a pluralityof burners provided severally with outlets, a duct with which saidburners communicate, means for supplying a mixture of air and fuel tosaid duct, flow-controlling means arranged to regulate the flow of themixture from the duct to said burners, means responsive to temperatureconditions within the furnace for adjusting said flow-controlling meansand regulating the pressure of the mixture flowing from the duct to saidburners, means for maintaining at substantially predetermined value theratio of air to fuel in said mixture while said flow-controlling meansare so adjusted in accordance with the temperature conditions within thefurnace, and means ineach burner, responsive to variations in thepressure of the mixture delivered to the burners for regulating the flowof the mixture through the outlets of the burners.

ing from the duct to said burners, means for maintaining atsubstantially predetermined value the ratio of air to fuel in saidmixture while said flow-controlling means are so adjusted in ac--cordance with the temperature conditions within the furnace, and meansfor the prevention of explosive back-firing in the system, said meansbeing organized with said burners severally and responsive to a drop inthe pressure of said mixture to critical value.

7. A pre-mix firing system for an industrial furnace including a burnerhaving an outlet in communication with the combustion chamber of burnerscommunicate, means for supplying a,

said furnace, a duct communicating with the burner, means formaintaining a mixture of air and fluid fuel in said duct,flow-controlling means arranged to regulate the flow of the mixture fromsaid duct to said burner, means responsive to temperature conditionswithin the furnace for adjusting the flow-controlling means andregulating the pressure of the mixture flowing from the duct to theburner, means for maintaining at substantially constant value the ratioof air to fuel in said mixture while the pressure of the mixture flowingto said burner is so regulated, and means responsive to variations inthe pressure of the mixture delivered to said burner for regulating thequantity of the mixture flowing through said burner outlet.

8. A pre-mix' firing systemfor an industrial furnace including a burnerhaving an outlet in communication with the combustion chamber of saidfurnace, a duct communicating with the burner, means. for maintaining amixture of air and fluid fuel in said duct, flow-controlling meansarranged to regulate the flow of the mixture from said duct to saidburner, means responsive to temperature conditions within the furnacefor adjusting the flow-controlling means and regulating the pressure ofthe mixture flowing from the duct to the burner, means for maintainingat substantially constant value the ratio of air to fuel in said mixturewhile the pressure of the mixture flowing to said burner is soregulated, and means organized with said burner for safeguarding theburner and the system from explosive back-firing of the mixture.

FREDERICK S. BLOOM.

